1. Field of the Invention
This invention relates a resolution conversion unit and an apparatus that has the resolution conversion unit that are used for enlarging/reducing an image by converting the number of pixels of the input image.
The term xe2x80x9cenlargingxe2x80x9d means the increment of the number of pixels per one direction in the case that a specified picture is expressed on an screen, and on the other hand the term xe2x80x9creducingxe2x80x9d means that decrement of the number of pixels per one direction in the case that a specified picture is expressed on an screen.
2. Related Art
The format (resolution) of the image signal has been diversified concomitantly with the appearance of the high-definition television and popularization of the computer that can process the image signal easily. It has been necessary that the receiver is rendered capable of enlarging or reducing an image so as to match with the indication given in the broadcast concomitantly with the diversification of the broadcasting service. Furthermore, it has been required that the image signal is exchanged between apparatuses having the different resolution concomitantly with realization of easy connection between apparatuses concomitantly with realization of digital apparatuses.
The resolution conversion of an image is described herein under.
The resolution conversion of an image and the enlargement/reduction of an image are an equivalent process in view of the conversion of the number of pixels. For example, a process in which an original image having a resolution composed of 720xc3x97480 pixels is converted to an image having a resolution composed of 1440xc3x97960 pixels is exemplified for description. The process involves doubling conversion of the number of pixels in both horizontal and vertical directions.
It is assumed that the image after conversion is projected on a screen having the same physical size as that of the image before conversion, then the process is regarded as the resolution conversion process because the number of pixels per unit length is doubled. On the other hand, it is assumed that the image after conversion is projected on a screen having the doubled physical size in both vertical and horizontal directions in comparison with the size of the screen on which the image before conversion is projected, then the process is regarded as the image enlargement process because the size of the image is doubled though the number of pixels per unit length is not converted.
Anyway, both processes are substantially equivalent in that an image composed of 720xc3x97480 pixels is converted into an image composed of 1440xc3x97960 pixels in the image process. Therefore, the resolution conversion of an image is not discriminated from the enlargement/reduction of an image hereinafter.
Various techniques have been proposed to realize the resolution conversion of the image signal, for example, U.S. Pat. No. 5,253,064 and U.S. Pat. No. 4,774,581 are proposed. These proposals are made to enlarge or reduce the image for an specified purpose, and do not intend the mutual conversion of the image having various resolution as described herein above, that is, do not intend the arbitrary enlargement and reduction by means of the systematic method.
In the conventional technique, it is required to use different algorithms for enlargement and reduction respectively in order to realize the arbitrary enlargement/reduction resolution conversion as described herein above. It is possible to provide respective hardware apparatuses exclusively used for these different algorithms. However, such structure is disadvantageous in that the large circuit scale is required. Though the hardware is partially commonly used for both enlargement and reduction with switching, the complicated control is required because different algorithms are used for enlargement and reduction respectively, and the partial common use of the hardware leads to a large circuit scale.
It is the object of the present invention to propose an algorithm that is capable of systematic both enlargement and reduction, and provides a resolution conversion unit and an apparatus having the resolution conversion unit that are capable of realizing the arbitrary enlargement/reduction with a relatively simple single hardware without the problem as described herein above by application of the algorithm.
To achieve the above-mentioned object, a resolution conversion unit in accordance with the present invention for converting the resolution of an input video signal with a magnification of M/N is provided with;
a storage means for storing the arithmetic result,
an arithmetic means including an adding means for adding a positive integer M to an output of the storage means and a subtracting means for subtracting a positive integer N from the output of the storage means,
a memory means for temporarily storing a video signal,
a memory control means for generating a reading and/or writing control signal based on the output supplied from the arithmetic means, and
a pixel value arithmetic means for calculating an output pixel value corresponding to the pixel value included in the input video signal based on the output supplied from the arithmetic means.